A crystal plasticity based approach to establish role of grain size and crystallographic texture in the Tension–Compression yield asymmetry and strain hardening behavior of a Magnesium–Silver–Rare Earth alloy

Existence of tension–compression yield asymmetry is a serious limitation to the load bearing capablities of Magnesium alloys in a number of light weight structural applications.The present work is aimed at nullifying the tension to compression asymmetry problem and strain hardening anomalies in a Magnesium–Silver–Rare Earth alloy by engineering different levels of microstructural conditions via friction stir processing and post process annealing.The existence and extent of yield asymmetry ratio in the range of microstructural conditions was experimentally obtained through quasistatic tensile and compression tests.The yield asymmetry problem was profoundly present in specimens of coarse grained microstructures when compared to their fine grained and ultra fine grained counterparts.The impact of the microstructure and associated mechanisms of plasticity on the macroscopic strain hardening behavior was established by Kock–Mecking’s analysis.Crystal plasticity simulations using Viscoplastic Self Consistency approach revealed the consequential role of extension twinning mechanism for the existence of yield asymmetry and anomalies in strain hardening behavior.This was especially dominant with coarsening of grain size.Electron Microscopy and characterization were conducted thoroughly in partially deformed specimens to confirm the predictions of the above simulations.The role of crystallographic texture for inducing the polarity to Tension–Compression yield asymmetry was corroborated.A critical grain size in Magnesium–Silver–Rare earth alloy was hereby established which could nullify influences of extension twinning in yield asymmetry ratio.

Microstructures and properties of Nb-Si-based alloys with B addition

The Nb-16Si-18Ti-xB(at%,similarly hereinafter,x=0,1,2,3)alloys were prepared by arc melting in a water-cooled copper crucible.The influences of B addition on their microstructures and properties were based on the data of X-ray diffraction(XRD),field emission scanning electron microscopy(FESEM),and electronic universal material testing machine.It is found that the addition of B promotes the formation ofα-Nb5Si3phase and suppresses the formation of Nb3Si phase.B addition also tends Nb-16Si-18Ti alloy to form the hypereutectic structures.The content of silicide phases shows a trend of firstly decreasing and then increasing in Nb-16Si-18Ti-xB(x=0,1,2,3)alloys.The size of Nb solid solution(Nbss)phase increases in Nb-16Si-18Ti-xB(x=0,1,2,3)alloys after heat treatment at 1523 K for 10 h.The room temperature compression strength of Nb-16Si-18Ti alloy increases firstly and then decreases with B addition.The high-temperature compression strength of Nb-16Si-18Ti alloy decreases firstly and then increases with B addition.It is found that the volume and size of silicide phases have a synergistic effect on the compression strength of Nb-TiSi-based alloys.